1. Field of the Invention
The present invention relates to a method of producing an L-amino acid selected from L-glutamic acid, L-arginine and L-threonine using a microorganism. L-glutamic acid and L-arginine are industrially useful as seasonings. L-threonine is useful for feed materials.
2. Brief Description of the Related Art
L-amino acids are typically produced industrially by fermentation methods in which a variety of microorganisms are used. For example, for the production of L-glutamic acid, coryneform L-glutamic acid-producing bacteria mainly belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or mutant strains thereof are used (Akashi, K. et al, Amino Acid Fermentation. Japan Scientific Societies Press, p. 195 to 215, 1986). Other microorganisms which can be used to produce L-glutamic acid by fermentation include microorganisms belonging to the genus Bacillus, Streptomyces, Penicillium or the like (Japanese Laid-Open Patent Publication No. 5-244970); microorganisms belonging to the genus Pseudomonas, Arthrobacter, Serratia, Candida or the like (U.S. Pat. No. 3,563,857); microorganisms belonging to the genus Bacillus, Pseudomonas or Serratia, Aerobacter aerogenes (currently Enterobacter aerogenes) or the like (Japanese Patent Publication (Kokai) No. 32-9393); or an Escherichia coli mutant strain or the like (Japanese Laid-Open Patent Publication No. 5-244970). In addition, microorganisms belonging to the genus Klebsiella, Erwinia, Pantoea or Enterobacter can also be used to produce L-glutamic acid by fermentation (Laimonis A. Laimins, Proc. Natl. Acad. Sci. USA, 1978 July; 75 (7): 3216-19; Laimonis A. Laimins, Proc. Natl. Acad. Sci. USA, 1981 January; 78 (1): 464-68; Mark O. Waldethaug, J. Bacteriol., 1992 April; 174 (7):2152-59).
In order to produce a substance of interest, such as an L-amino acid, by fermentation using the above-mentioned microorganisms, for example, wild-type microorganisms (wild-type strain), or auxotrophic strains derived from a wild-type strain, metabolic regulation mutant strains derived from a wild-type strain, such as a drug-resistant mutant strain, or a method in which a strain having both characteristics of autotrophic strain and metabolic regulation mutant strain can be used.
Furthermore, in recent years, recombinant DNA technology has been employed in fermentation production of a substance of interest. For example, L-amino acid productivity of a microorganism is improved by enhancing the expression of a gene encoding an L-amino acid biosynthetic enzyme (U.S. Pat. No. 5,168,056 and U.S. Pat. No. 5,776,736), or by enhancing the influx of a carbon source into the L-amino acid biosynthetic pathway (U.S. Pat. No. 5,906,925).
On the basis of sequence analyses and the like, the protein YdcI, which has been reported to be native to bacteria of the Enterobacteriaceae family, including Escherichia coli, is presumed to be a LysR-type transcription factor (Keseler, I. M. et al., “EcoCyc: A comprehensive database resource for Escherichia coli.” Nucleic Acids Res. 2005, Vol. 33, D334-337; Encyclopedia of Escherichia coli K-12 Genes and Metabolism, [online], [searched on Apr. 12, 2007], Internet <URL://ecocyc.org/>). In Escherichia coli, YdcI is encoded by the ydcI gene (Riley, M. et al., “Escherichia coli K-12: a cooperatively developed annotation snapshot-2005”, Nucleic Acids Res. 2006, Vol. 34, 1-9). Production of L-lysine, L-threonine, and L-tryptophan using a bacterium in which ydcI gene is enhanced has been reported (Japanese Patent Application No. 2007-141802); however, for L-threonine, this patent document does not demonstrate the effect of a strain in which the ydcI gene is amplified. There has also been no report of L-amino acid production using an ydcI gene-deficient bacterium.